FTTR active equipment: Main FTTR + Sub FTTR. PAM4 is a four-level pulse amplitude-modulated signal, which can be electrical or optical. Previous generations of serial data standards used non-return-to-zero (NRZ) encoding, rendering bits distinct high- and. PAM4 (4-level pulse amplitude modulation) is being adopted in many applications at data rates of 50 Gb/s and higher. Main FTTR is used to connect to the internet, supporting Ethernet or Fiber uplink. Leisure (Karaoke, Bar, Teahouse. Add security detection mechanism 1.